It is well known that light radiation having a wavelength of between 280 and 320 nm causes erythema and skin bums, the effects of which increase according to the length of exposure. A suitable protective agent should accordingly absorb light radiation in the zone from about 280 to 320 nm. "Emulsions," as used herein, is a system which includes a liquid (e.g. an oil) dispersed in an immersible liquid (e.g. water). As such, an emulsion has two phases, a continuous phase and a discontinuous phase. In the case of an oil-in-water emulsion, oil is the discontinuous phase, and water is the continuous phase. Hydrophobic constituents of the emulsion tend to concentrate in the oil phase, while hydrophilic constituents tend to concentrate in the water (or aqueous) phase. Water-in-oil emulsions have been described for use as vehicles for sunscreen agents. When water-in-oil emulsions are applied to the skin, the water-phase droplets are believed to be suspended in a film of oil. This film is believed to create a moisturizing and non-hygroscopic barrier, which does not take up water, thus deterring the emulsion from being washed off.
U.S. Pat. No. 4,284,630 to Yu et al. (Aug. 18, 1981) discloses stable water-in-oil emulsions useful as vehicles for cosmetics or for application of medicinal compositions. The emulsions use magnesium oxide or magnesium hydroxide as a stabilizing agent, which permit the incorporation of up to 70% water in the total composition without loss of shelf-life stability. The emulsions create a water non-washable dispersion medium, which possess substantiation and occlusion properties after application to the skin.
U.S. Pat. No. 4,781,914 to Deckner (Nov. 1, 1988) discloses a moisture-resistant skin treatment composition in the form of a sprayable oil-in-water emulsion that inverts to a water-in-oil emulsion upon being robbed onto the skin. The invention uses polyglyceril-8 oleate as an emulsifier to impart moisture resistance to the skin treatment composition.
U.S. Pat. No. 5,256,422 to Albert et al. (Oct. 26, 1993) discloses a water-in-oil emulsion having a discontinuous aqueous phase dispersed within a continuous oil phase. The aqueous droplets forming the discontinuous aqueous phase have intact liposomes dispersed therein, thus forming a type of oil-in-water-in-oil emulsion. The invention allows incorporation of aqueous soluble materials into either the aqueous phase external to the lipid vesicles or into the lipid vesicles themselves. Likewise, any oil soluble materials can be included into the emulsion via the continuous oil phase or the lipid vesicles.
Sunscreen preparations, which extend the time of exposure needed to produce a sunburn, are also commercially available. Such preparations contain ultraviolet absorbing chemicals such as the alkyl esters of aminosalicylic acid disclosed in U.S. Pat. No. 4,036,951 to Halpern et al. (Jul. 19, 1977), the benzoxazole derivatives in U.S. Pat. No. 4,250,315 to Poncioni (Feb. 10, 1981), and the coffee bean oil in U.S. Pat. No. 4,793,990 to Grollier et al. (Dec. 27, 1988).
Physical sunscreens generally include heavy creams or pastes containing such compounds as ZnO and TiO.sub.2. Although physical sunscreens reflect and scatter radiation effectively, such sunscreens create an opaque film and thus lack cosmetic appeal.
The art is not believed to suggest that by carefully choosing various ingredients and incorporating them into specific phases of a selected emulsion that a synergistic combination would result.